U.S. patent application number 15/778425 was filed with the patent office on 2018-12-06 for process for the epoxidation of propene.
This patent application is currently assigned to Evonik Degussa GmbH. The applicant listed for this patent is EVONIK DEGUSSA GMBH, THYSSENKRUPP INDUSTRIAL SOLUTIONS AG. Invention is credited to Manfred BARZ, Marc BRENDEL, Hans-Christian DIETZ, Thomas HAAS, Willi HOFEN, Bernd JAEGER, Michael KLEIBER, Barbel KOLBE, Wolfgang WOLL.
Application Number | 20180346432 15/778425 |
Document ID | / |
Family ID | 54705120 |
Filed Date | 2018-12-06 |
United States Patent
Application |
20180346432 |
Kind Code |
A1 |
HOFEN; Willi ; et
al. |
December 6, 2018 |
PROCESS FOR THE EPOXIDATION OF PROPENE
Abstract
In a process for the epoxidation of propene, comprising the
steps of reacting propene with hydrogen peroxide, separating
propene oxide and a recovered propene stream from the reaction
mixture, separating propane from all or a part of the recovered
propene stream in a C3 splitter column, and passing the overhead
product stream of the C3 splitter column to the epoxidation step, a
propane starting material with a propane fraction of from 0.002 to
0.10 is used, the epoxidation is operated to provide a propane
fraction in the reaction mixture of from 0.05 to 0.20 and the C3
splitter column is operated to provide an overhead product stream
which comprises a propane fraction of at least 0.04 in order to
reduce the size and the energy consumption of the C3 splitter
column.
Inventors: |
HOFEN; Willi; (Rodenbach,
DE) ; HAAS; Thomas; (Munster, DE) ; WOLL;
Wolfgang; (Maintal, DE) ; KOLBE; Barbel;
(Witten, DE) ; DIETZ; Hans-Christian;
(Hattersheim, DE) ; BRENDEL; Marc; (Bruchkobel,
DE) ; JAEGER; Bernd; (Bickenback, DE) ; BARZ;
Manfred; (Freigericht, DE) ; KLEIBER; Michael;
(Hattersheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EVONIK DEGUSSA GMBH
THYSSENKRUPP INDUSTRIAL SOLUTIONS AG |
Essen
Essen |
|
DE
DE |
|
|
Assignee: |
Evonik Degussa GmbH
Essen
DE
ThyssenKrupp Industrial Solutions AG
Essen
DE
|
Family ID: |
54705120 |
Appl. No.: |
15/778425 |
Filed: |
November 25, 2016 |
PCT Filed: |
November 25, 2016 |
PCT NO: |
PCT/EP2016/078770 |
371 Date: |
May 23, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07D 301/32 20130101;
B01D 3/14 20130101; C07D 301/12 20130101; B01J 23/30 20130101; B01D
2257/7022 20130101; B01J 29/7049 20130101; B01D 2257/80
20130101 |
International
Class: |
C07D 301/12 20060101
C07D301/12; C07D 301/32 20060101 C07D301/32; B01D 3/14 20060101
B01D003/14; B01J 29/70 20060101 B01J029/70 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 2015 |
EP |
15196510.0 |
Claims
1-16. (canceled)
17. A process for the epoxidation of propene, comprising the steps:
a) continuously reacting propene with hydrogen peroxide in the
presence of an epoxidation catalyst, using propene in molar excess
to hydrogen peroxide, to provide a reaction mixture comprising
propene oxide, non-reacted propene and propane; b) separating
propene oxide and a recovered propene stream with a total content
of propene and propane of more than 90% by weight from the reaction
mixture obtained in step a); c) feeding all or a part of said
recovered propene stream to a C3 splitter column for separating
propene and propane and withdrawing an overhead product stream
depleted in propane with regard to said recovered propene stream
and a bottoms product stream enriched in propane with regard to
said recovered propene stream from said column; and d) passing the
overhead product stream obtained in step c) to step a); wherein a
propene starting material containing propane with a mass ratio of
propane to the combined amount of propene and propane of from 0.002
to 0.10 is fed to said process for the epoxidation of propene, the
reaction mixture provided in step a) comprises propane with a mass
ratio of propane to the combined amount of propene and propane of
from 0.05 to 0.20 and the overhead product stream withdrawn from
the C3 splitter column comprises propane with a mass ratio of
propane to the combined amount of propene and propane of at least
0.04.
18. The process of claim 17, wherein said overhead product stream
withdrawn from the C3 splitter column has a higher mass ratio of
propane to the combined amount of propene and propane than said
propene starting material.
19. The process of claim 17, wherein said recovered propene stream
is fed to the C3 splitter column as a liquid to a feed point in the
upper third of the C3 splitter column.
20. The process of claim 17, wherein all or a part of said propene
starting material is fed to said C3 splitter column.
21. The process of claim 20, wherein said propene starting material
is fed as liquid to said C3 splitter column at a feed point above
the feed point for the recovered propene stream.
22. The process claim 17, wherein step b) comprises separating said
recovered propene stream as an overhead product in a C3 rectifier
column from a bottoms product comprising propene oxide, and feeding
all or a part of said propene starting material to said C3
rectifier column.
23. The process of claim 22, wherein said propene starting material
is fed as liquid to said C3 rectifier column at a feed point less
than 10 theoretical stages from the column top.
24. The process of claim 17, wherein a part of said recovered
propene stream is fed to said C3 splitter column and the remainder
is passed to step a).
25. The process of claim 24, wherein the fraction of said recovered
propene stream that is fed to said C3 splitter column is adjusted
to maintain a constant mass ratio of propane to the combined amount
of propene and propane in the recovered propene stream.
26. The process of claim 24, wherein from 1 to 50% by weight of
said recovered propene stream is fed to said C3 splitter
column.
27. The process of claim 17, wherein said bottoms product stream
has a mass ratio of propane to the combined amount of propene and
propane of at least 0.8.
28. The process of claim 17, wherein in step a) the initial molar
ratio of propene to hydrogen peroxide is from 3 to 5.
29. The process of claim 17, wherein in step a) the epoxidation
catalyst is a titanium zeolite containing titanium atoms on silicon
lattice positions.
30. The process of claim 17, wherein in step a) the epoxidation
catalyst is a homogeneous catalyst selected from
heteropolytungstates and manganese chelate complexes.
31. The process of claim 30, wherein the homogeneous catalyst is a
quaternary ammonium salt of a polytungstophosphate.
32. The process of claim 30, wherein the homogeneous catalyst is a
manganese complex comprising at least one
1,4,7-trimethyl-1,4,7-triazacyclonane ligand.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for the
epoxidation of propene with hydrogen peroxide in which a propene
starting material containing propane can be used efficiently.
BACKGROUND OF THE INVENTION
[0002] The epoxidation of propene with hydrogen peroxide in the
presence of an epoxidation catalyst is usually carried out with a
molar excess of propene relative to hydrogen peroxide in order to
avoid hydrogen peroxide decomposition and to achieve high
selectivities for propene oxide. Epoxidation of propene with a
heterogeneous titanium silicalite catalyst is known from EP 0 100
119 A1. Epoxidation of propene with a homogeneous manganese
catalyst is known from WO 2011/063937. Epoxidation of propene with
a homogeneous tungstophosphate catalyst is known from U.S. Pat. No.
5,274,140.
[0003] For an efficient use of propene, non-reacted propene has to
be recovered from the reaction mixture of the epoxidation reaction
and recycled to the epoxidation reaction. Commercial propene grades
usually contain propane as an impurity due to the manufacturing
processes used for making propene. Since the epoxidation catalysts
used for epoxidizing propene have little or no activity for
oxidizing propane, the use of a propene grade containing propane in
an epoxidation process with a propene recycle will lead to
accumulation of propane in the process. Efficient recycling of
propene then requires a separation of propane from propene and a
purge of propane from the process.
[0004] WO 2005/103024 discloses the use of a conventional C3
splitter column for separating propane from a mixture of propene
and propane recovered from an offgas from an epoxidation process
before recycling the propene to the epoxidation. Such a
conventional C3 splitter column has to be operated with a high
reflux ratio which leads to a high energy consumption.
[0005] WO 2004/018088 discloses recovery of propene and propane
from a gaseous propylene oxide process purge stream by absorption
in liquid propane followed by separation in a C3 splitter column,
providing an overhead vapor stream containing 31.2% by weight
propene and 65.2% by weight propane which is recycled to propylene
oxide production. However, due to the high propane content in the
recycle stream this method leads to a high accumulation of propane
in the process that requires considerably larger equipment for the
epoxidation reaction and the reaction mixture workup and increases
energy consumption in the reaction mixture workup.
[0006] Therefore, there is still a need for a process for the
epoxidation of propene with hydrogen peroxide in which a propene
starting material containing propane can be used and propane can be
purged from the process with less equipment and energy
consumption.
SUMMARY OF THE INVENTION
[0007] It has now been found that when operating the epoxidation to
provide a propane fraction in the non-reacted propene of from 0.05
to 0.20 and recovering non-reacted propene in a C3 splitter column
operated to provide a vapor at the column top with a propane
fraction of at least 0.04, the extra expense for larger equipment
for the epoxidation reaction and the reaction mixture workup and
increased energy consumption in the reaction mixture workup is more
than compensated by a reduced equipment size and energy consumption
of the C3 splitter column when compared to a conventionally
operated C3 splitter column.
[0008] Subject of the invention is therefore a process for the
epoxidation of propene, comprising the steps [0009] a) continuously
reacting propene with hydrogen peroxide in the presence of an
epoxidation catalyst, using propene in molar excess to hydrogen
peroxide, to provide a reaction mixture comprising propene oxide,
non-reacted propene and propane; [0010] b) separating propene oxide
and a recovered propene stream with a total content of propene and
propane of more than 90% by weight from the reaction mixture
obtained in step a); [0011] c) feeding all or a part of said
recovered propene stream to a C3 splitter column for separating
propene and propane and withdrawing an overhead product stream
depleted in propane with regard to said recovered propene stream
and a bottoms product stream enriched in propane with regard to
said recovered propene stream from said column; and [0012] d)
passing the overhead product stream obtained in step c) to step a);
wherein a propene starting material containing propane with a mass
ratio of propane to the combined amount of propene and propane of
from 0.002 to 0.10 is fed to the process for the epoxidation of
propene; the reaction mixture provided in step a) comprises propane
with a mass ratio of propane to the combined amount of propene and
propane of from 0.05 to 0.20; and the overhead product stream
withdrawn from the C3 splitter column comprises propane with a mass
ratio of propane to the combined amount of propene and propane of
at least 0.04.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIGS. 1 to 3 show preferred embodiments of the process of
the invention.
[0014] FIG. 1 shows an embodiment where the propene starting
material is fed directly to reaction step a).
[0015] FIG. 2 shows an embodiment where the propene starting
material is fed as liquid to a feed point less than 10 theoretical
stages below the top of the C3 splitter column.
[0016] FIG. 3 shows an embodiment where the propene starting
material is fed to a C3 rectifier column of step b).
DETAILED DESCRIPTION OF THE INVENTION
[0017] The process of the invention uses a propene starting
material which contains propane with a mass ratio of propane to the
combined amount of propene and propane of from 0.002 to 0.10. The
mass ratio is preferably from 0.003 to 0.08 and most preferably
from 0.004 to 0.05. The propene starting material preferably
contains less than 1% by weight of components other than propene
and propane, more preferably less than 0.1% by weight. Suitable as
propene starting material are commercial products of chemical grade
propene and of polymer grade propene.
[0018] In step a) of the process of the invention, propene is
continuously reacted in a reaction step with hydrogen peroxide in
the presence of an epoxidation catalyst to provide a reaction
mixture containing propene oxide, non-reacted propene and propane.
Propene is used in excess to hydrogen peroxide, preferably with an
initial molar ratio of propene to hydrogen peroxide of from 1.1:1
to 30:1, more preferably 2:1 to 10:1 and most preferably 3:1 to
5:1. Propene is preferably used in an excess sufficient to maintain
an additional liquid phase rich in propene throughout step a).
Using an excess of propene provides high reaction rate and hydrogen
peroxide conversion and at the same time high selectivity for
propene oxide.
[0019] Hydrogen peroxide can be used as an aqueous solution,
preferably containing from 30 to 75% by weight hydrogen peroxide
and most preferably from 40 to 70% by weight.
[0020] The epoxidation catalyst can be a homogeneous catalyst or a
heterogeneous catalyst. Suitable homogeneous epoxidation catalysts
are manganese complexes with polydentate nitrogen ligands, in
particular 1,4,7-trimethyl-1,4,7-triazacyclononane ligands, as
known from WO 2011/063937. Other suitable homogeneous epoxidation
catalysts are heteropolytungstates and heteropolymolybdates, in
particular polytungstophosphates, as known from U.S. Pat. No.
5,274,140, preferably quaternary ammonium salts of a
polytungstophosphate. Suitable heterogeneous epoxidation catalysts
are titanium zeolites containing titanium atoms on silicon lattice
positions. Preferably, a titanium silicalite catalyst is used,
preferably with an MFI or MEL crystal structure. Most preferably a
titanium silicalite 1 catalyst with MFI structure as known from EP
0 100 119 A1, is used. The titanium silicalite catalyst is
preferably employed as a shaped catalyst in the form of granules,
extrudates or shaped bodies. For the shaping process the catalyst
may contain 1 to 99% of a binder or carrier material, all binders
and carrier materials being suitable that do not react with
hydrogen peroxide or with propene oxide under the reaction
conditions employed for the epoxidation, silica being preferred as
binder. Extrudates with a diameter of 1 to 5 mm are preferably used
as fixed bed catalysts.
[0021] When the epoxidation catalyst is a titanium silicalite, the
propene feed is preferably reacted with hydrogen peroxide in a
methanol solvent to provide a liquid reaction mixture comprising
methanol. The methanol solvent can be a technical grade methanol, a
solvent stream recovered in the workup of the epoxidation reaction
mixture or a mixture of both. The epoxidation reaction is then
preferably carried out at a temperature of 30 to 80.degree. C.,
more preferably at 40 to 60.degree. C., and at a pressure of from
1.9 to 5.0 MPa, more preferably 2.1 to 3.6 MPa and most preferably
2.4 to 2.8 MPa. The epoxidation reaction is preferably carried out
with addition of ammonia to improve propene oxide selectivity as
described in EP 0 230 949 A2. Ammonia is preferably added in an
amount of from 100 to 3000 ppm based on the weight of hydrogen
peroxide. The epoxidation is preferably carried out in a fixed bed
reactor by passing a mixture comprising propene, hydrogen peroxide
and methanol over a fixed bed comprising a shaped titanium
silicalite catalyst. The fixed bed reactor is preferably equipped
with cooling means and cooled with a liquid cooling medium.
Preferably, a cooled tube bundle reactor is used with the catalyst
fixed bed arranged within the tubes and a temperature profile along
the tube axis with temperatures within a range of less than
5.degree. C. along at least 80% of the length of the catalyst fixed
bed is maintained by cooling. The epoxidation reaction mixture is
preferably passed through the catalyst bed in down flow mode,
preferably with a superficial velocity from 1 to 100 m/h, more
preferably 5 to 50 m/h, most preferred 5 to 30 m/h. The superficial
velocity is defined as the ratio of volume flow rate/cross section
of the catalyst bed. Additionally it is preferred to pass the
reaction mixture through the catalyst bed with a liquid hourly
space velocity (LHSV) from 1 to 20 h.sup.-1, preferably 1.3 to 15
h.sup.-1. It is particularly preferred to maintain the catalyst bed
in a trickle bed state during the epoxidation reaction. Suitable
conditions for maintaining the trickle bed state during the
epoxidation reaction are disclosed in WO 02/085873 on page 8 line
23 to page 9 line 15. The methanol solvent is preferably used in
the epoxidation in a weight ratio of 0.5 to 20 relative to the
amount of aqueous hydrogen peroxide solution. The amount of
catalyst employed may be varied within wide limits and is
preferably chosen so that a hydrogen peroxide consumption of more
than 90%, preferably more than 95%, is achieved within 1 minute to
5 hours under the employed epoxidation reaction conditions. Most
preferably, the epoxidation reaction is carried out with a catalyst
fixed bed maintained in a trickle bed state at a pressure close to
the vapor pressure of propene at the reaction temperature, using an
excess of propene that provides a reaction mixture comprising two
liquid phases, a methanol rich phase and a propene rich liquid
phase. Two or more fixed bed reactors may be operated in parallel
or in series in order to be able to operate the epoxidation process
continuously when regenerating the epoxidation catalyst.
Regeneration of the epoxidation catalyst can be carried out by
calcination, by treatment with a heated gas, preferably an oxygen
containing gas or by a solvent wash, preferably by the periodic
regeneration described in WO 2005/000827.
[0022] In step a) the propene is reacted in the presence of propane
introduced into the process of the invention with the propene
starting material. The amount of propane passed to step a) and the
initial molar ratio of propene to hydrogen peroxide are chosen so
that the reaction mixture provided in step a) comprises propane
with a mass ratio of propane to the combined amount of propene and
propane of from 0.05 to 0.20, preferably from 0.10 to 0.15.
[0023] In step b) of the process of the invention, propene oxide
and a recovered propene stream are separated from the reaction
mixture obtained in step a). The separation is carried out to
provide a recovered propene stream with a total content of propene
and propane of more than 90% by weight, preferably more than 95% by
weight. The separation of propene oxide and of the recovered
propene stream can be carried out by methods known from the art,
such as by distillation. Separation step b) preferably comprises a
step of separating propene with an overhead product in a C3
rectifier column from a bottoms product comprising propene oxide.
Preferably, all or a part of the overhead product of the C3
rectifier column is withdrawn as recovered propene stream.
[0024] In step b) the reaction mixture is preferably subjected to a
pressure reduction. Propene vapor formed by the pressure reduction
may be recompressed and cooled to provide the recovered propene
stream by condensation. Preferably, the propene vapor formed by the
pressure reduction is recompressed and the compressed propene vapor
is fed to a C3 rectifier column where it is separated to provide
the recovered propene stream as the overhead product and a bottoms
product comprising propene oxide and other components having a
boiling point higher than propene, such as a solvent. The bottoms
product can be combined with the liquid mixture remaining after the
pressure reduction.
[0025] When methanol is used as solvent, the liquid mixture
remaining after the pressure reduction is preferably separated by
distillation in a pre-separation column to provide an overhead
product comprising propene oxide, methanol and residual propene and
a bottoms product comprising methanol, water and non-reacted
hydrogen peroxide. The pre-separation column is preferably operated
to provide an overhead product comprising from 20 to 60% of the
methanol contained in the liquid phase of the last pressure
reduction step. The pre-separation column preferably has from 5 to
20 theoretical separation stages in the stripping section and less
than 3 theoretical separation stages in a rectifying section and is
most preferably operated without reflux and without a rectifying
section to minimize the residence time of propene oxide in the
pre-separation column. The pre-separation column is preferably
operated at a pressure of from 0.16 to 0.3 MPa. Propene oxide and
methanol are condensed from the overhead product of the
pre-separation column and propene is preferably stripped from the
resulting condensate in a propene stripping column which provides a
bottom stream comprising propene oxide and methanol which is
essentially free of propene. Propene oxide is preferably separated
from the bottoms stream of the propene stripping column in an
extractive distillation using water as the extraction solvent. The
extractive distillation is preferably operated with additional
feeding of a reactive compound containing an unsubstituted NH.sub.2
group and capable of reacting with acetaldehyde during the
extractive distillation, as described in WO 2004/048335. Extractive
distillation with a reactive compound provides a high purity
propene oxide containing less than 50 ppm of carbonyl
compounds.
[0026] In step c) of the process of the invention, all or a part of
the recovered propene stream is fed to a C3 splitter column for
separating propene and propane and an overhead product stream
depleted in propane with regard to the recovered propene stream and
a bottoms product stream enriched in propane with regard to the
recovered propene stream are withdrawn from the column. The
recovered propene stream is preferably fed to the C3 splitter
column as a liquid to a feed point in the upper third of the C3
splitter column. The feed point is preferably less than 35
theoretical stages, more preferably less than 20 theoretical stages
below the column top. When no other material is fed to the C3
splitter column, the recovered propene stream is preferably fed as
a liquid at the uppermost stage of the column. The C3 splitter
column may comprise discrete trays or column packings.
[0027] The C3 splitter column is operated to provide an overhead
product stream which comprises propane with a mass ratio of propane
to the combined amount of propene and propane of at least 0.04,
preferably of from 0.04 to 0.15, more preferably of from 0.05 to
0.12. The desired propane fraction in the overhead product stream
may be achieved by adjusting the number of separation stages in the
rectifying section between the feed point of the recovered propene
stream and the column top and by adjusting the reflux ratio of the
column. The C3 splitter column is preferably operated to provide an
overhead product stream which has a higher mass ratio of propane to
the combined amount of propene and propane than the propene
starting material. Operating the C3 splitter column to provide an
overhead product stream having a higher propane fraction than the
propene starting material allows for increasing the propane content
in the recovered propene stream, which allows the use of a smaller
C3 splitter column and reduces the energy consumption for operating
the column.
[0028] The C3 splitter column is preferably operated to provide a
bottoms product stream which has a mass ratio of propane to the
combined amount of propene and propane of at least 0.8, preferably
of from 0.9 to 0.98.
[0029] In step d) of the process of the invention, the overhead
product stream obtained in step c) is passed to step a).
[0030] Preferably, only a part of the recovered propene stream is
fed to the C3 splitter column in step c) and the remainder is
passed to step a). More preferably, from 1 to 50% by weight of the
recovered propene stream is fed to the C3 splitter column and the
remainder is passed to step a). The fraction of the recovered
propene stream that is fed to the C3 splitter column is preferably
adjusted to maintain a constant mass ratio of propane to the
combined amount of propene and propane in the recovered propene
stream. Feeding only a part of the recovered propene stream to the
C3 splitter column allows the use of a smaller size C3 splitter
column and recycling a part of the recovered propene stream
directly into the epoxidation reaction increases the propane
content in the reaction mixture and in the recovered propene
stream, which allows the use of a C3 splitter column having fewer
separation stages and operation of the column at a lower reflux
ratio which saves energy.
[0031] In the process of the invention, the propene starting
material may be fed to different stages.
[0032] The propene starting material may be fed directly to step a)
of the process.
[0033] In a preferred embodiment, all or a part of the propene
starting material is fed to the C3 splitter column of step c).
Preferably, at least 20% and more preferably at least 50% of the
propene starting material is fed to the C3 splitter column of step
c) and the remainder is fed to step a), step b) or both. Most
preferably, all propene starting material is fed to the C3 splitter
column of step c). In this embodiment, the C3 splitter column is
preferably operated to provide an overhead product stream which has
a higher mass ratio of propane to the combined amount of propene
and propane than the propene starting material. Operating the C3
splitter column to provide a vapor having a higher propane fraction
than the propene starting material has the advantage that the
propene starting material fed to the C3 splitter column can replace
all or part of the column reflux which reduces the energy
consumption of the C3 splitter column. The propene starting
material is preferably fed as liquid to the C3 splitter column at a
feed point above the feed point for the recovered propene stream.
Feeding propene starting material to the C3 splitter column has the
advantage of removing non-volatile and high boiling impurities from
the propene starting material without the need for extra equipment.
When the propene starting material contains no significant amount
of C4+ hydrocarbons, i.e. hydrocarbons having 4 or more carbon
atoms, the propene starting material is preferably fed to the
uppermost tray or to the top of the uppermost packing of the C3
splitter column. This embodiment may also be used to remove C4+
hydrocarbons with the C3 splitter column bottoms product when a
propene starting material comprising substantial amounts of C4+
hydrocarbons is used. A propene starting material containing
significant amounts of C4+ hydrocarbons is preferably fed to the C3
splitter column at a feed point at least one theoretical stage
below the column top, preferably 5 to 12 theoretical stages below
the column top, in order to provide an overhead product stream with
a low content of C4+ hydrocarbons.
[0034] In another preferred embodiment of the process of the
invention, step b) comprises separating the recovered propene
stream as an overhead product in a C3 rectifier column from a
bottoms product comprising propene oxide, and all or a part of the
propene starting material is fed to the C3 rectifier column.
Preferably, at least 20% and more preferably at least 50% of the
propene starting material is fed to the C3 rectifier column and the
remainder is fed to the C3 splitter column of step c). The propene
starting material is preferably fed as liquid to the C3 rectifier
column at a feed point less than 10 theoretical stages from the
column top. Preferably, the propene starting material is fed to the
uppermost tray or to the top of the uppermost packing of the C3
rectifier column. In this embodiment, the recovered propene stream
is preferably fed as a liquid to the uppermost stage of the C3
splitter column. Feeding propene starting material to the C3
rectifier column has the advantage of removing non-volatile and
high boiling impurities from the propene starting material without
increasing the size or the energy consumption of the C3 splitter
column. This embodiment is preferably employed when a propene
starting material is used which comprises only small amounts of C4+
hydrocarbons. Feeding propene starting material to the C3 rectifier
column allows to further reduce the size and the energy consumption
of the C3 splitter column compared to feeding propene starting
material directly to the C3 splitter column.
[0035] FIGS. 1 to 3 show preferred embodiments of the process of
the invention.
[0036] FIG. 1 shows an embodiment where the propene starting
material is fed directly to reaction step a). In this embodiment,
the propene starting material (1), hydrogen peroxide (2) and a
methanol solvent (3) are fed to a reaction step (4), where propene
and hydrogen peroxide are reacted in the presence of an epoxidation
catalyst to provide a reaction mixture (5) comprising propene
oxide, non-reacted propene, propane, methanol solvent and water.
This reaction mixture is separated in a separation step (6) into a
recovered propene stream (7), a propene oxide product (8), a stream
of recovered methanol solvent (9) which is recycled to the reaction
step (4), and an aqueous stream (10). A part of the recovered
propene stream (7) is fed to a C3 splitter column (11) at a feed
point (12) in the upper third of the C3 splitter column (11) and
the remainder of the recovered propene stream (7) is recycled to
the reaction step (4). The C3 splitter column (11) provides an
overhead product stream (13), depleted in propane with regard to
the recovered propene stream (7), which is passed to the reaction
step (4), and a bottoms product stream (14), enriched in propane
with regard to the recovered propene stream (7).
[0037] The embodiment of FIG. 2 differs from the embodiment of FIG.
1 in that the propene starting material (1) is fed as liquid to a
feed point (15) above the feed point (12) for the recovered propene
stream instead of being fed to the reaction step (4). Feeding the
propene starting material in liquid form near the top of the C3
splitter column prevents high boiling and non-volatile impurities
of the propene starting material from contaminating the epoxidation
catalyst and allows operation of the C3 splitter column with a low
reflux ratio which saves energy. This embodiment is advantageous
when the propene starting material contains significant amounts of
C4+ hydrocarbons, because removal of C4+ hydrocarbons in the C3
splitter column prevents C4+ olefins contained in the propene
starting material from being epoxidized in the reaction step and
avoids problems in separating the propene oxide product (8) from
C4+ hydrocarbons having a boiling point close to the boiling point
of propene oxide.
[0038] The embodiment of FIG. 3 differs from the embodiment of FIG.
2 in that the propene starting material (1) is not fed to the C3
splitter column, but to a C3 rectifier column (not shown) of the
separation step (6), in which C3 rectifier column the recovered
propene stream (7) is separated as an overhead stream from a
bottoms product comprising propene oxide. Feeding the propene
starting material to a C3 rectifier column of separation step (6)
prevents high boiling and non-volatile impurities of the propene
starting material from contaminating the epoxidation catalyst,
allows the use of a small sized C3 splitter column and reduces the
energy consumption for propane removal. This embodiment is
advantageous when the propene starting material contains only small
amounts of C4+ hydrocarbons.
LIST OF REFERENCE SIGNS
[0039] 1 Propene starting material [0040] 2 Hydrogen peroxide
[0041] 3 Methanol solvent [0042] 4 Reaction step [0043] 5 Reaction
mixture [0044] 6 Separation step [0045] 7 Recovered propene stream
[0046] 8 Propene oxide product [0047] 9 Recovered methanol solvent
[0048] 10 Aqueous stream [0049] 11 C3 splitter column [0050] 12
Feed point for recovered propene [0051] 13 Overhead product stream
depleted in propane [0052] 14 Bottoms product stream enriched in
propane [0053] 15 Feed point for propene starting material
EXAMPLES
Example 1
Propene Starting Material Fed to C3 Splitter Column
[0054] For the embodiment of FIG. 2 and an epoxidation with a
titanium silicalite catalyst and a methanol solvent providing a
reaction mixture containing 28.2% by weight propene and 3.7% by
weight propane, the design and operation parameters of the C3
splitter column were calculated with the program Aspen Plus.RTM. of
Aspen Technology varying the fraction of recovered propene fed to
the C3 Splitter column. The calculations were performed for a
propene starting material containing 97.5% by weight propene and
2.5% by weight propane. 32.5 t/h liquid propene starting material
is fed to the top of a C3 splitter column having 101 theoretical
stages operated at 2.3 MPa. The reaction step a) and the separation
step b) provide a recovered propene stream of 135 t/h containing
87.2% by weight of propene and 11.5% by weight of propane. A
fraction of this recovered propene stream given in table 1 is fed
to the 12.sup.th theoretical stage of the C3 splitter column
(counted from column top). The remaining part of recovered propene
stream is combined with the overhead product stream of the C3
Splitter column and recycled to reaction step a). A bottoms product
is withdrawn from the C3 Splitter column at a rate of 0.973 t/h and
the reflux ratio is adjusted to provide a propene content of 7.8%
by weight in the bottoms product. Table 1 gives the feed rate of
recovered propene to the C3 Splitter Column and the calculated
values for the mass fraction of propane in the overhead product
stream, the reflux ratio, the reboiler duty (power consumed for
evaporation) and the column diameter.
TABLE-US-00001 TABLE 1 Calculation results for C3 splitter column
with propene starting material fed to C3 splitter column Recovered
Mass fraction propene fedto of propane Reboiler Column C3 splitter
in overhead duty Reflux diameter column in t/h product stream in kW
ratio in m 15 0.037 11322 1.711 5.69 20 0.045 8503 0.822 4.32 25
0.051 7571 0.472 3.90 30 0.056 7226 0.287 3.75 35 0.061 7098 0.167
3.70 40 0.065 7059 0.078 3.68
[0055] The calculation results demonstrate that operating the C3
splitter column to provide a mass ratio of propane to the combined
amount of propene and propane of at least 0.04 in the overhead
product stream reduces the size of the column and the energy needed
for operating the column.
Example 2
Propene Starting Material Fed to C3 Rectifier Column
[0056] The calculations of example 1 were repeated, but instead of
feeding the propene starting material to the C3 splitter column,
the liquid propene starting material is fed to the first
theoretical stage (counted from the column top) of a C3 rectifier
column of separation step b), providing as overhead product a
recovered propene stream of 167 t/h containing 87.2% by weight of
propene and 11.5% by weight of propane, a fraction of which is fed
as liquid to the top of the C3 splitter column. Table 2 gives the
feed rate of recovered propene to the C3 splitter column and the
calculated values for the mass fraction of propane in the overhead
product stream of the C3 splitter column, the reflux ratio, the
reboiler duty (power consumed for evaporation) and the column
diameter.
TABLE-US-00002 TABLE 2 Calculation results for C3 splitter column
with propene starting material fed to C3 rectifier column Mass
fraction Recovered of propane propene fedto in C3 splitter Reboiler
Column C3 splitter column overhead duty Reflux diameter column in
t/h product stream in kW ratio in m 10 0.033 30192 39.591 13.79 12
0.048 17898 18.371 8.55 20 0.078 9935 5.039 4.99 30 0.091 8124
2.191 4.15 40 0.098 7441 1.159 3.85 50 0.102 7081 0.629 3.69 60
0.104 6856 0.306 3.60 70 0.106 6703 0.090 3.53
[0057] The calculation results demonstrate that feeding the
starting material to a rectifier column of step b) may further
reduce the size of the C3 splitter column and the energy needed for
operating the column compared to feeding the starting material to
the C3 splitter column.
Example 3
Propene Starting Material Fed to C3 Rectifier Column
[0058] The calculations of example 2 were repeated for feeding 70
t/h recovered propene stream to the C3 splitter column and
providing an overhead product stream with a mass fraction of
propane of 0.106, varying the feed point to the C3 splitter column.
Table 3 gives the feed point in theoretical stages from the top of
the C3 splitter column and the calculated values for the reflux
ratio, the reboiler duty (power consumed for evaporation) and the
column diameter.
TABLE-US-00003 TABLE 3 Calculation results for C3 splitter column
with propene starting material fed to C3 rectifier column and
variation of feed point to C3 splitter column Feed point for
recovered Reboiler Column propene in theoretical duty Reflux
diameter stages from column top in kW ratio in m 1 6703 0.090 3.53
7 6862 0.116 3.60 12 7126 0.160 3.71 20 7820 0.274 4.01
[0059] The calculation results demonstrate that for the embodiment
where the propene starting material is fed to a C3 rectifier
column, feeding the recovered propene to the C3 splitter column at
or near the column top reduces the size of the C3 splitter column
and the energy needed for operating the column.
Example 4
Propene Starting Material Fed Directly to Reaction Step a)
[0060] The calculation of example 1 was repeated for the embodiment
of FIG. 1, feeding the liquid propene starting material to the
epoxidation reaction and feeding the entire recovered propene
stream to the 12.sup.th theoretical stage of the C3 splitter column
(counted from column top). A bottoms product is withdrawn from the
C3 Splitter column at a rate of 0.968 t/h with a propene content of
1.4% by weight in the bottoms product and 131.5 t/h overhead
product with a mass fraction of propane in the overhead product
stream of 0.110 are recycled to the reaction step to provide the
same composition of the reaction mixture as in example 1. A
reboiler duty (power consumed for evaporation) of 12577 kW and a
column diameter of 6.30 m were calculated for this process
configuration.
Example 5 (Comparative)
Propene Starting Material Fed Directly to Reaction Step a)
[0061] The calculation of example 4 was repeated for recycling an
overhead stream from the C3 splitter column having the same propane
content of 2.5% by weight as the propene starting material. The
lower propane content in the recycled propene stream leads to a
lower mass ratio of propane to the combined amount of propene and
propane in the reaction mixture and a recovered propene stream of
121 t/h containing 3.1% by weight of propane. A bottoms product is
withdrawn from the C3 Splitter column at a rate of 1.285 t/h with a
propene content of 5.9% by weight in the bottoms product and 119.5
t/h overhead product with a mass fraction of propane in the
overhead product stream of 0.025 are recycled to the reaction step.
A reboiler duty (power consumed for evaporation) of 45101 kW and a
column diameter of 20.0 m were calculated for this process
configuration.
Example 6
Propene Starting Material Fed Directly to Reaction Step a)
[0062] The calculation of example 4 was repeated for a propene
starting material containing 95.0% by weight propene and 5.0% by
weight propane, feeding 33.3 t/h liquid propene starting material
to the epoxidation reaction. A bottoms product is withdrawn from
the C3 Splitter column at a rate of 1.933 t/h with a propene
content of 3.9% by weight in the bottoms product and 130.5 t/h
overhead product with a mass fraction of propane in the overhead
product stream of 0.104 are recycled to the reaction step to
provide the same composition of the reaction mixture as in example
1. A reboiler duty (power consumed for evaporation) of 16552 kW and
a column diameter of 8.01 m were calculated for this process
configuration.
Example 7 (Comparative)
Propene Starting Material Fed Directly to Reaction Step a)
[0063] The calculation of example 5 was repeated for a propene
starting material containing 95.0% by weight propene and 5.0% by
weight propane, feeding 33.3 t/h liquid propene starting material
to the epoxidation reaction. The lower propane content in the
recycled propene stream leads to a lower mass ratio of propane to
the combined amount of propene and propane in the reaction mixture
and a recovered propene stream of 125 t/h containing 6.2% by weight
of propane. A bottoms product is withdrawn from the C3 Splitter
column at a rate of 2.120 t/h with a propene content of 3.6% by
weight in the bottoms product and 122.7 t/h overhead product with a
mass fraction of propane in the overhead product stream of 0.05 are
recycled to the reaction step. A reboiler duty (power consumed for
evaporation) of 39413 kW and a column diameter of 17.8 m were
calculated for this process configuration.
[0064] Examples 4 to 7 demonstrate that operating the C3 splitter
column to provide an overhead product stream which has a higher
mass ratio of propane to the combined amount of propene and propane
than the propene starting material reduces the size of the C3
splitter column and the energy needed for operating the column.
* * * * *